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1.
Diel vertical migration (DVM) and seasonal timing of three sympatricCancer spp. larvae were investigated in southeastern Alaska. Diel sampling was conducted at a station in Icy Strait at 0400, 0700, 1000, 1300 h in the first day, and 1300, 1600, 1900, and 2200 h in the second day from June to September 2001. Larvae were collected with Bongo nets (333 and 505 μm mesh) towed vertically from 20 m depth to the surface. During flood tides surface temperature increased slightly and salinity decreased; the reverse occurred during ebb tides. Zooplankton biomasses were higher in the early morning and evening than during the midday. A total of 4,482 larvae were examined for the study.Cancer oregonensis larvae were most abundant (4,238), followed byC. magister (205) andC. productus (39). Larval density peaked in June while no larvae were found in September.C. magister larvae had a crepuscular migration; larval abundance peaked in early morning and evening.C. oregonensis larvae comprised 94.6% of allCancer spp. larvae collected and had a strong DVM in June. Earlier zoeal stages ofC. oregonensis were relatively more abundant during midday, while later stages were more abundant at night. In July, later larval stages ofC. oregonensis were distributed at the surface all day with a peak at 2200 h. Larvae ofC. productus first occurred in July and peaked in August.C. productus had DVM but many were at the surface diurnally.C. magister andC. oregonensis larvae co-occurred seasonally as they do in the lower latitudes, e.g., Washington and British Columbia; however,C. productus appeared approximately 2 mo later thanC. magister andC. oregonensis in southeastern Alaska.  相似文献   

2.
Seasonal occurrence and vertical distribution of larvae of two genera of brachyuran crab were studied in a secondary estuary flowing into Delaware Bay. Spawning in the xanthid crabRhithropanopeus harrisii occurred earlier with peak abundance of larvae in June and with a distinct decline in abundance in August. In contrast,Uca spp. larvae reached peak abundance in August. All zoeal stages ofR. harrisii were collected in the river suggesting that larvae of this species are retained in secondary estuaries near areas of prime adult habitat. Only zoea stage I larvae and megalopa ofUca spp. were collected in the river indicating that larvae of these speies may be flushed into the Delaware Bay and may not return to secondary estuaries near areas suitable for adult habitat until the megalopa stage is reached. It is not clear if this dispersal pattern is an active or passive process. *** DIRECT SUPPORT *** A01BY019 00004  相似文献   

3.
This study investigates the influence ofPhragmites australis (common reed) invasion on the habitat of the resident marsh fish,Fundulus heteroclitus (mummichog) in the Hackensack Meadowlands, New Jersey. These abundant fish play an important role in the transfer of energy from the marsh surface to adjacent subtidal waters and thus estuarine food webs. The objectives of this 2-yr study (1999 and 2000) were to compare the distribution and abundance of the eggs, larvae, juveniles, and adults of mummichog and their invertebrate prey inhabitingSpartina alterniflora-dominated marshes withPhragmites-dominated marshes, and to experimentally investigate the influence of marsh surface microtoprography on larval fish abundance withinPhragmites-dominated marshes. In 2000, we verified that egg deposition does occur inPhragmites-dominated marshes. In both years, the abundance of larvae and small juveniles (4–20 mm TL) inS. alterniflora was significantly greater than inPhragmites-dominated marshes, while larger juveniles and adults (>20 mm TL) were similarly abundant in both habitat types. The overall abundance of larvae and small juveniles was significantly greater in experimentalPhragmites plots in which microtopography was manipulated to resemble that ofSpartina marshes than inPhragmites control plots. Major groups of invertebrate taxa differed between marsh types with potential prey for larval fish being significantly more abundant inS. alterniflora marshes.Phragmites-dominated marshes may not provide the most suitable habitat for the early life-history stages of the mummichog. The low abundance of larvae and small juveniles inPhragmites marshes is likely due to inadequate larval habitat and perhaps decreased prey availability for these early life history stages.  相似文献   

4.
Synoptic ichthyoplankton sampling was conducted on two transects, one on either side of Beaufort Inlet, North Carolina, during the winter immigration season of seven ocean-spawned, estuarine-dependent fishes;Brevoortia tyrannus (Atlantic menhaden),Leiostomus xanthurus (spot),Micropogonias undulatus (Atlantic croaker),Lagodon rhomboides (pinfish),Paralichthys albigutta (Gulf flounder),P. dentatus (summer flounder), andP. lethostigma (southern flounder). Densities and lengths of larvae were significantly different among sampling dates, with distance offshore, and between sides of the inlet. Flood-tide stage had minimal effect on larval densities and lengths except forP. albigutta andP. lethostigma. Changes in larval densities with distance offshore were not coherent among species; densities ofB. tyrammus increased offshore whereas densities of the other species decreased offshore. Average larval densities on a sampling date were coherent among species. Patterns in larval lengths were also coherent among the four non-flounder species. Larval densities outside of Beaufort Inlet were correlated with larval densities inside of Beaufort Inlet. Larval densities outside of Beaufort Inlet were also correlated with the north component of the wind, nearshore water temperature, and distance to the mid-shelf front. Differences in larval density across the inlet were significantly correlated with the east component of the wind. The patterns in larval densities outside of Beaufort Inlet were complex and apparently influenced by both the physical processes that supply larvae to the nearshore region and nearshore physical dynamics.  相似文献   

5.
A multivariate analytical strategy is proposed for aiding the investigator in extracting maximum information from environmental data. Data are carefully coded and scaled and are tested for redundancy using R-mode cluster analysis. The samples are partitioned into environmental classes using Q-mode cluster analysis. Q-mode ordination facilitates interpretations, which usually can be verified by comparison with field relationships. Discriminant analysis serves as an identification procedure for extending the classification to unknown samples. The strategy is demonstrated by application to Cape Hatteras microorganism distributions and Devonian sedimentary facies.  相似文献   

6.
Feeding habits ofMenidia peninsulae were analyzed monthly over a one year period and compared to planktonic prey available at the capture site. Three feeding stages were found: (1) In early spring, young-of-the-year fed on tychoplankton and detritus. (2) From late spring through winter,M. peninsulae preyed selectively on calanoid copepods and cypris larvae. (3) GravidM. peninsulae fed primarily on amphipods and larval silversides. In the Crystal River area,M. peninsulae reproduce in early spring. Silversides apparently migrate from the higher salinity bays to the lower salinity marshes in the summer, and then move back into the bays in fall.  相似文献   

7.
Pollen and charcoal analysis of radiocarbon-dated sediment cores from Duck Pond in the Cape Cod National Seashore provide a continuous 12,000-yr vegetation and climate history of outer Cape Cod. A Picea-Hudsonia parkland and then a Picea-Pinus banksiana-Alnus crispa boreal forest association grew near the site between 12,000 and 10,000 yr B.P. This vegetation was replaced by a northern conifer forest of Pinus strobus-P. banksiana, and, subsequently, by a more mesophytic forest (Pinus strobus, Tsuga, Quercus, Fagus, Acer, Ulmus, Fraxinus, Ostrya) as the climate became warmer and wetter by 9500 yr B.P. By 9000 yr B.P. a Pinus rigida-Quercus association dominated the landscape. High charcoal frequencies from this and subsequent levels suggest that the pine barrens association developed during a warmer and drier climate that lasted from 9000 to about 5000 yr B.P. Increased percentages of Pinus strobus pollen indicate a return to moister and cooler conditions by about 3500 yr B.P. A doubled sedimentation rate, increased charcoal, and increased herb pollen suggest land disturbance near the pond before European settlement. These results suggest a rapid warming in the northeast in the early Holocene and support a hypothesis of a rapid sea level rise at that time. Comparison of the pollen results from Duck Pond with those from Rogers Lake, Connecticut, illustrates the importance of edaphic factors in determining the disturbance frequency and vegetation history of an area.  相似文献   

8.
This paper presents the first paleostress results obtained from displacement and fracture systems within the Lower Eocene sediments at Jabal Hafit, Abu Dhabi Emirate, UAE. Detailed investigation of Paleogene structures at Jabal Hafit reveal the existence of both extensional structures (normal faults) and compressional structures (strike-slip and reverse faults). Structural analysis and paleostress reconstructions show that the Paleogene kinematic history is characterized by the succession of four paleostress stages. Orientation of principal stresses was found from fault-slip data using an improved right-dihedra method, followed by rotational optimisation (TENSOR program).The paleostress results confirm four transtensional tectonic stages (T1–T4) which affected the study area. The first tectonic stage (T1) is characterized by SHmax NW–SE σ2-orientation. This stage produced NW–SE striking joints (tension veins) and E–W to ENE–WSW striking dextral strike-slip faults. The proposed age of this stage is Early Eocene. The second stage (T2) had SHmax N–S σ2-orientation. N–S striking joints and NNE–SSW striking sinistral strike-slip faults, E–W striking reverse faults and N–S striking normal faults were created during this stage. The T2 stage is interpreted to be post-Early Eocene in age. The third stage (T3) is characterized by SHmax E–W σ2-orientation. This stage reactivated the E–W reverse faults as sinistral strike-slip faults and created E–W striking joints and NE–SW reverse faults. The proposed age for T3 is post-Middle Eocene. During the T3 (SHmax E–W σ2-orientation) stage the NNW-plunging Hafit anticline was formed. The last tectonic stage that affected the study area (T4) is characterized by SHmax NE–SW σ2-orientation. During this stage, the ENE–WSW faults were reactivated as sinistral strike-slip and reverse faults. NE–SW oriented joints were also created during the T4 (SHmax NE–SW σ2-orientation) stage. The interpreted age of this stage is post-Middle Miocene time but younger than T3 (SHmax E–W σ2-orientation) stage.  相似文献   

9.
Striped bass,Morone saxatilis, larvae of 9 DAH (days after hatching) were fed for 16 d with five densities of adults (5–100 l?1), copepodites (10–200 l?1), and nauplii (50–1,000?1) of the copepodEurytemora affinis, and 5-DAH and 10-DAH larvae were fed at seven densities (5–500 l?1) of brine shrimp,Artemia salina, nauplii. The study determined the effects of prey types and densities on the survival and growth of the fish larvae, and the effects of delaying first feeding from 5 DAH to 10 DAH. The survival and grwoth of the larvae fedE. affinis adults was higher than those fedE. affinis copepodites.E. affinis nauplii were the poorest prey. OneE. affinis adult provided nutrition equivalent to 1.45 copepoditer or 11.12 nauplii. The percentage survival of the larvae was higher for those fedA. salina nauplii thanE. affinis adults at the densities below 67.25 l?1, but there was no difference at this density or higher. Delaying first feeding from 5 DAH to 10 DAH did not affect percentage survival and size of larvae at the end of the experiments. Because the survival and growth of the larvae increased as the prey density increased, it was difficult to set a point along the regression line as the minimum density requirement level. It may be said that for striped bass larvae, the higher the prey density, the higher the survival and growth, and thus the greater the recruitment success.  相似文献   

10.
Fundulus luciae was collected for a year at Fox Creek Marsh and, occasionally, at other salt marshes along the York River, Virginia. It occurred in high intertidal areas in brackish, sometimes oxygen deficient shallow ditches, mudholes and tidal rivulets located in stands ofSpartina alterniflora. Preserved specimens were examined to determine the reproductive season, fecundity, diet and associated metazoan parasites of the species. Developing ova were present from mid-April to mid-August and exhibited a broad size range; the number of large ova (>1.6 mm diameter) never exceeded 16 per female. Stomach contents consisted mainly of detritus, diatoms, ostracods, dipterans and copepods. All major metazoan parasite groups except Cestoda were represented onF. luciae; Monogenea were most numerous, with 57.2% incidence. Eggs and larvae were described. Preserved larvae ofF. luciae were distinguished from those ofF. heteroclitus by their dorsal pigmentation pattern. It was concluded thatF. luciae, a purportedly rare species, is not rare, but probably restricted to high intertidal salt marshes where it may have been previously overlooked.  相似文献   

11.
The Atlantic menhaden,Brevoortia tyrannus, is an abundant plankton-feeding fish that undertakes extensive seasonal migrations, moving from overwintering locations offshore south of Cape Hatteras to the mid-Atlantic Bight and New England inshore waters during spring and summer. A bioenergetic model, based on field and laboratory studies, shows that when large numbers of menhaden enter Narragansett Bay, Rhode Island, during spring and early summer, they significantly influence plankton populations through size-selective grazing and nutrient regeneration. A population biomass of 9.1×106 kg of menhaden feeding for 12 h each day in the upper bay would result, in a substantial reduction of the instantaneous growth rate of the >20-μm phytoplankton. Instantaneous growth rates of zooplankton would be negative if the same population of menhaden was present, resulting in a reduction in the biomass of zooplankton. Given the ambient phytoplankton and zooplankton populations, menhaden could achieve the seasonal growth measured in Narragansett Bay during 1976 by feeding on average about 5 h d?1. Daily nitrogen excretion rates of the 9.1×106 kg menhaden population were 56.4% of the mean standing stock of ammonia-N in the upper bay. Because menhaden travel in schools their effects are likely to be intense but strongly localized, increasing spatial heterogeneity in the ecosystem. When the fish migrate southward in the fall they transfer between 3.3% and 6.2% of the nitrogen exported annually from the bay.  相似文献   

12.
The behavior of the leatherjack, Oligoplites saurus, was studied in the field. Four behavioral patterns were identified: (1) cleaning behavior on the redfin needlefish, Strongylura notata, (2) intraspecific schooling, (3) interspecific schooling with the rough and tidewater silversides, Membras martinica and Menidia peninsulae, pinfish, Lagodon rhomboides, and menhaden, Brevoortia sp., (4) swimming along in a “leafmimic” position or next to floating algae or debris. Fishes exhibiting any of these behaviors fed primarily on plankton. Schooling leatherjackets also fed on scales of Strongylurus notata, Brevoortia sp., Menidia peninsulae and Lagodon rhomboides. These observations are supported by stomach content analyses. It is suggested that scale-feeding may be a preadaptation for cleaning behavior among leatherjackets.  相似文献   

13.
Sun Hole, a small fissure cave on the north side of Cheddar Gorge, Somerset, is best known as the site where late Upper Palaeolithic artefacts are associated with human and other mammal remains that immediately pre-date the Lateglacial interstadial. These remains from the upper levels (Unit I) overlie sediments (Unit II) that are thought to have accumulated during a full glacial period, below which are sediments (Unit III) attributed to an interglacial stage. The extinct land snail Retinella (Lyrodiscus) sp., which in Britain was only known from the Hoxnian Stage, had previously been recovered from Unit III. The interglacial at the base of the sequence was therefore assigned to the Hoxnian Stage (Marine Isotope Stage (MIS) 11, 424–374 kyr). Here we provide additional analyses of samples from Unit III, which as well as containing further Retinella (Lyrodiscus), also yielded a specimen of Monachoides incarnatus, its first record from the British Pleistocene. An associated assemblage of small mammals included a few that are rare in the British Pleistocene, such as birch mouse (Sicista cf. betulina) and garden dormouse (Eliomys quercinus). The vole Lasiopodomys gregaloides and the shrew Sorex (Drepanosorex) savini do not occur as late as the Hoxnian and therefore suggest an older age in the early Middle Pleistocene. The record from Sun Hole therefore has parallels with the well-known sequence from the upper Calcareous Member in the nearby cavern system at Westbury-sub-Mendip.  相似文献   

14.
Previous work on the genetics ofCyathura polita populations along the Atlantic coast indicated that northern and southern populations have diverged significantly. We used starch gel electrophoresis to study the transition between northern and southern populations for gene frequencies at four enzyme loci.Cyathura from three sites in the Carolinas were compared with those from representative populations in the north (Massachusetts) and south (Florida).Cyathura polita from the northern and southern populations were fixed for different alleles at three of the four loci assayed.C. polita from a population in North Carolina had the northern electromorph for two loci and were polymorphic at theEst locus for the northern and southern electromorphs, whileC. polita from a population in South Carolina had the southern electromorphs for two loci and were polymorphic at theMdh-1 locus for northern and southern electromorphs. Thus, there appears to be gene flow between the genetically differentiated populations in the north and south. One population ofCyathura from North Carolina had unique electromorphs at the four loci assayed and appears to be a new species.  相似文献   

15.
It is shown in the short comment that the sea levels are oscillating about a longer-term trend and that the sea level rise (SLR) computed with time windows of 20, 30 or 60?years also oscillates, with the amplitude of these latter oscillations reducing as the time window increases. The use of only two values of the SLR distribution is misleading to infer conclusions about the accelerating behaviour. In particular, the comparison of the 30-year SLR 1950?C1979 with the 30-year SLR 1980?C2009 for the tide gauges along the Atlantic coast of North America north of Cape Hatteras to infer an accelerating behaviour is particularly wrong because the 30-year time window is a too short interval to appreciate the longer-term sea level trend cleared of the multi-decadal oscillations, and the two values from the SLR distribution are computed, respectively, at the times of a valley and a peak for the 60-year Atlantic Ocean multi-decadal oscillation. By using a 60-year time window or all the data since opening when more than 60?years of recording are available and by analysing the SLR time history, the only conclusion that can be inferred from the analysis of the tide gauges along the North American Atlantic coast is that the sea levels are oscillating without too much of a positive acceleration along their longer-term trend.  相似文献   

16.
This paper explores the size and arrival of tsunamis in Oregon and Washington from the most likely partial ruptures of the Cascadia subduction zone (CSZ) in order to determine (1) how quickly tsunami height declines away from sources, (2) evacuation time before significant inundation, and (3) extent of felt shaking that would trigger evacuation. According to interpretations of offshore turbidite deposits, the most frequent partial ruptures are of the southern CSZ. Combined recurrence of ruptures extending ~490 km from Cape Mendocino, California, to Waldport, Oregon (segment C) and ~320 km from Cape Mendocino to Cape Blanco, Oregon (segment D), is ~530 years. This recurrence is similar to frequency of full-margin ruptures on the CSZ inferred from paleoseismic data and to frequency of the largest distant tsunami sources threatening Washington and Oregon, ~M w 9.2 earthquakes from the Gulf of Alaska. Simulated segment C and D ruptures produce relatively low-amplitude tsunamis north of source areas, even for extreme (20 m) peak slip on segment C. More than ~70 km north of segments C and D, the first tsunami arrival at the 10-m water depth has an amplitude of <1.9 m. The largest waves are trapped edge waves with amplitude ≤4.2 m that arrive ≥2 h after the earthquake. MM V–VI shaking could trigger evacuation of educated populaces as far north as Newport, Oregon for segment D events and Grays Harbor, Washington for segment C events. The NOAA and local warning systems will be the only warning at greater distances from sources.  相似文献   

17.
Aspects of the population dynamics of the polychaeteSabellaria vulgaris Verrill 1874 were studied by observing the temporal occurrence of larvae in the plankton of Delaware Bay. Vertical plankton samples were collected monthly from July 1970 to October 1971. Four 25-hour plankton studies were conducted within this time period, and on one occasion samples were collected on a transect across the mouth of the bay.Sabellaria vulgaris larvae were present in the bay only from mid-April through October. July (1970) and August (1971) 25-hour plankton studies showed larvae present in the water column at virtually all times of the day and night. Horizontal dispersion of larvae in the plankton was clearly aggregated. However, correlation of larval presence, absence or abundance with the measured physical factors in the estuary was not apparent except on a seasonal scale. Six developmental stages were defined based upon observation of laboratory-reared larvae. Young larvae appeared in the plankton on numerous occasions, indicating that spawning occurred repeatedly during the April–October time period in Delaware Bay. Relative to other habitats within the geographic range ofS. vulgaris, Delaware Bay is a particularly well-suited environment for the construction of massive colonies by the species. Adults living in large aggregates would exhibit greater fitness because of the higher probability of eggs being fertilized. Indications are that a portion of the larvae produced in the Bay are retained in the estuary and undergo settlement there. Delaware Bay may be a population center for the species. A comparison of reproductive phenomena among sabellariid species is presented. It is apparent that the species,S. vulgaris, consists of several physiologically distinct populations, and that this is true of certain other sabellariid species as well.  相似文献   

18.
Variation in morphological characters used to distinguish the three sympatric species ofPalaemonetes, i.e.,P. pugio, P. intermedius, andP. vulgaris, is suggestive of natural hybridization. Interspecific crosses among the species and intraspecific crosses of allopatric populations ofP. pugio were made to determine whether hybridization was feasible and to evaluate taxonomic characters of the juveniles. No interspecific matings produced larvae in the laboratory. Larvae, from intraspecific matings ofP. pugio andP. vulgaris were reared to 40 days of age. Larval survival rates, development time, and postlarval length ofP. pugio andP. vulgaris were not different, but juveniles ofP. pugio at 40 days after hatching were larger than those ofP. vulgaris. At 40 daysP. pugio had developed adult diagnostic features. However,P. vulgaris displayed sufficient variation in adult diagnostic features to resembleP. pugio in some cases. The intraspecific matings ofP. pugio from widely separated populations were fertile, but there was some indication of reduced reproductive compatibility in crosses involving Virginia females and Florida males relative to intrapopulational controls. *** DIRECT SUPPORT *** A01BY019 00002  相似文献   

19.
Sampling theC. septemspinosa population of the Mystic River Estuary simultaneously in deep water and along the shoreline indicated that this population has two major reproductive periods. Berried females move into the estuary in early spring and late autumn to hatch their eggs. Two-and three-year-old females produce the larvae in the spring and 1.0- to 1.5-year-old females give rise to the larvae in winter. All larvae are carried seaward by the tidal currents and eventually settle as juveniles in the deep water near the mouth of the estuary or on the continental shelf. Juveniles from the spring hatch migrate to the shallow shoreline where they grow, rapidly, 0.15 mg/day. Those that hatch during the late autumn do not migrate shoreward. A model of this life cycle and evidence to support two recruitment mechanisms that involve inshore migration of adults and the offshore drift of the larvae are presented.  相似文献   

20.
The seasonal abundance and spatial distribution of eggs and early larvae of the bay anchovy,Anchoa mitchilli, and the weakfish,Cynoscion regalis, were determined from plankton collections taken during 1971–1976 in the lower Chesapeake Bay. Eggs and larvae of the bay anchovy,Anchoa mitchilli, dominated the ichthyoplankton, making up 96% of the total eggs and 88% of all larvae taken. A comparison of egg and larval densities from the lower Chesapeake Bay to existing data from other East Coast estuaries suggested that Chesapeake Bay is a major center of spawning activity for this species.Anchoa mitchilli spawning commenced in May when mean water column temperatures approached 17°C and abruptly ceased after August. Eggs and early larvae presented a continuous distribution throughout the study area during these months. Eggs and larvae of several sciaenid species, especiallyC. regalis, ranked second in numerical abundance. Larval weakfish were consistently taken in late summer of each sampling year but peak abundance and distribution was observed in August 1971. Sciaenid eggs exhibited a distinct polyhaline distribution with greatest concentrations observed at the Chesapeake Bay entrance or along the Bay eastern margin. Analysis of sciaenid egg morphometry and larval occurrence suggested spawning activity of at least four species. Additional important species represented by eggs and/or larvae in the lower Chesapeake Bay wereHypsoblennius hentzi, Gobiosoma ginsburgi, Trinectes maculatus, Symphurus plagiusa andParalichthys dentatus with the remaining species occurring infrequently.  相似文献   

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